Field
The present invention relates to an internal current collection method that uses an internal current collection structure including a plurality of current collectors, among methods for collecting current in a tubular thermal to electric converting cell. The internal current collection method of the thermal to electric converting cell includes a porous current collector which easily contacts with an internal electrode of the thermal to electric converting cell and a lead wire which is a conductive medium and fastened to the porous current collector.
Description of Related Art
Alkali Metal Thermal to Electric Converter (AMTEC) is a thermal to electric power generator capable of generating electrical energy from thermal energy.
When a temperature difference is given to both ends of an ionically conductive Beta-Alumina Solid Electrolyte (BASE), Na charged in the cell is ionized into Na+ due to the vapor pressure difference of Na and is diffused from anode to cathode through the electrolyte, and then is neutralized.
In this case, low voltage and high current are generated. So, when the cells are modularized by being connected in series or in parallel, a large amount of electric power can be generated.
The development of AMTEC technology has started for the purpose of an electric power source for space. The AMTEC has a high power density per unit area and high efficiency, and maintains stability.
The AMTEC uses a variety of heat sources, for example, solar energy, fossil fuel, waste heat, terrestrial heat, nuclear reactor, etc. The AMTEC is comprised of electric power generation cells capable of generating electricity without using a driver such as a turbine, a motor or the like, so that it can directly generate electricity from a portion contacting with the heat. When the AMTEC is formed in the form of a module in series or in parallel, a great amount of electricity of several KW to several hundredths MW can be generated.
The form of waste heat includes flue gas, exhaust air, waste hot water, waste steam and the like. Sensible heat and reaction heat of a product of the production process are also classified into the waste heat. In the collection of the waste heat, there are a variety of forms, standards and materials, etc., of a heat exchanger which is applicable in accordance with the temperature of the waste heat, the condition of flow rate of the waste heat and whether or not the waste heat includes a corrosive material.
A device using the waste heat includes a waste heat collector, an electric heat exchanger, a heat pipe type heat exchanger and the like. In a special case, a separate collection system is considered.
The AMTEC is capable of improving the efficiency by directly generating high-quality electricity from the heat source. Therefore, the AMTEC is now issued as a promising technology replacing the existing power generation technologies, for example, hydro power generation, terminal power generation, nuclear power generation, tidal power generation, wind power generation and so on.
One of the features of the AMTEC power generation technology is to have a structure simpler than that of other thermoelectric conversion devices and to have high energy conversion efficiency.
In particular, compared with a solar thermal power plant, the AMTEC does not require a mechanical driving part like a turbine, etc. Compared with a thermoelectric device, the AMTEC can be applied to a high-capacity, high-efficiency system.
The process of generating electricity in the AMTEC will be specifically described. After the state of Na vapor is changed into a vapor state in a high temperature and high pressure evaporator by a heat source, Na+ passes through beta-alumina solid electrolyte (BASE), and free electrons return to a cathode through an electric load from an anode, and then are recombined with ion generated from the surface of a low temperature and low pressure BETA and then is neutralized. Electricity is generated during this process.
The vapor pressure of Na plays the most significant role in a thermal to electric power generator as an energy source or a driving force which generates electricity. Also, free electrons generated during a process in which Na passes through the solid electrolyte due to a concentration difference and temperature difference of a working fluid are collected through electrodes, so that electricity can be generated.
The beta-alumina and Na super-ionic conductor (NASICON) may be used as the solid electrolyte.
However, the NASICON has a problem in its stability of crystal structure when it is exposed to high temperature for a long time.
The beta-alumina includes two kinds of beta′-alumina and beta″-alumina.
The beta″-alumina has a more improved layer structure so that the conductivity of the Na+ ion is much better. Therefore, the beta″-alumina is now generally used.
A process is repeated in which the neutral Na vapor is condensed by being cooled on the inner surface of a low pressure condenser and is transferred to an evaporator by a capillary wick, and then is changed into a vapor state again. Generally, the temperature of the evaporator is in a range of 900 K to 1,100 K, and the temperature of the condenser in a range of 500 K to 600 K.
It is possible for the efficiency of the thermal to electric power generation of the AMTEC to be up to 40%. The AMTEC has a high power density and a simple structure without a separate driving part.
A tubular cell used in the thermal to electric converting cell of the AMTEC is generally composed of an internal electrode, an electrolyte, and an external electrode. Here, for the purpose of collecting electricity generated by the cell, the internal electrode and the external electrode are required to be electrically connected to each other by means of a conductor. However, the internal electrode formed on the inner surface of the tubular cell is technically difficult to electrically connect.
With regard to a tubular solid oxide fuel cell (SOFC), a cylindrical current collector has been used in the past. However, with regard to the AMTEC, a current collector thereof has not been clearly disclosed yet.
The conventional technology increases the weights of the unit cell and system and requires a high manufacturing cost. This may be a factor that reduces an economical efficiency and power density per unit weight.